An important objective in the design of many electronic systems is to reduce or limit power consumption. For example, most portable computers are designed with the capability to employ one or more power management techniques to extend battery life. One such power management technique is to remove power from an electronic device within the portable computer when that device is expected to be idle for a certain period of time. At least two approaches to removing power from a specific electronic device in a portable computer have been used. These two approaches are illustrated in FIGS. 1a and 1b.
FIG. 1b is a simplified block diagram of portable computer 100 including power supply 101, voltage regulator 102, electronic device 103, and power management controller 104. Electronic device 103 receives a stable supply voltage through voltage input terminal 105. Voltage regulator 102 provides the stable supply voltage on output voltage terminal 106. Voltage input terminal 107 of voltage regulator 102 is coupled through switch 108 to power supply output terminal 109 of power supply 101. Switch 108 is controlled by power management controller 104 such that power is removed from voltage regulator 102, and therefore from electronic device 103, when a control signal provided on control signal output terminal 110 is asserted.
One problem with the approach illustrated in FIG. 1a is that the time required to restore the stable supply voltage to electronic device 103 includes a delay between the time that power is restored to voltage regulator 102 and the time that voltage regulator 102 provides a stable supply voltage on output voltage terminal 106. This delay typically includes the time required to charge an output capacitor within voltage regulator 102. This problem can be avoided with the approach illustrated in FIG. 1b.
FIG. 1b is a simplified block diagram of portable computer 150 including power supply 151, voltage regulator 152, electronic device 153, and power management controller 154. Electronic device 153 receives a stable supply voltage through voltage input terminal 155. Voltage regulator 152 provides the stable supply voltage on output voltage terminal 156. Voltage input terminal 157 of voltage regulator 152 is coupled to power supply output terminal 158 of power supply 151. Switch 159 is controlled by power management controller 154 such that power is removed from electronic device 153, but not voltage regulator 152, when a control signal provided on control signal output terminal 160 is asserted.
One problem with the approach illustrated in FIG. 1b is that voltage regulator 152 continues to consume power even when electronic device 153 is idle. In response to this problem, a novel approach to reducing the power consumption of a voltage regulator has been developed.